In recent years, disk storage apparatuses have exhibited dramatically increased recording densities. Hard disk drives (HDDs) are known as typical disk storage apparatuses. For increased recording density on the magnetic disk of the HDD, a magnetic head must be positioned as close to the surface of the magnetic disk (magnetic disk medium) as possible to the extent that the magnetic head does not contact with the magnetic disk. That is, it is necessary to reduce as much as possible the distance (spacing) between the magnetic head (hereinafter referred to as the head) and the magnetic disk (hereinafter referred to as the disk). Such spacing is also referred to as the head flying height.
To regulate the head flying height, a heater element is provided in the head. When predetermined power (heater power) is supplied to the heater element, the heater element produces heat and thus thermally deforms (expands) the head. The thermal deformation causes the head to project toward the surface of the disk and thus sets the head flying height to a target value.
However, a reduced head flying height increases the probability that the head (more specifically, a write element and a read element provided in the head) will contact (collide) with a very small protrusion (that is, a protruding defect) on the disk. Such contact may degrade the characteristics of the write and read elements.
Thus, the conventional technique determines a concentric circular area (that is, a track range) including a protrusion-like defect on the disk and a peripheral area thereof to be a non-use area (hereinafter referred to as a track skip area) that is not used to store data. No tracks within the track skip area are used for writing or reading; these tracks are skipped. According to the conventional technique, when, in a seek operation of moving the head from the current position to a target track, the head needs to be moved in a direction across the track skip area, the heater element is turned off. This avoids thermal deformation of the head. In this case, a projecting state of the head is expected to be released to avoid a possible contact between the head and the protrusion.
However, a certain time is needed to completely release the projecting state of the head. Thus, if the track skip area fails to be set to include an extra space, the head may reach the protrusion before the projecting state of the head is released in response to turn-off of the heater element. In such a case, the head contacts (collides) with the protrusion. On the other hand, if the track skip area is set to include an extra space, such contact as described above can be avoided. However, this setting reduces the format efficiency of the disk.